The invention relates to a safety insert for use with a tire to detect when the tire is resting on the safety insert. The safety insert warns the driver as soon as the tire starts to rest on it following a puncture or in the event of significant loss of pressure.
The purpose of these safety inserts, which in general are mounted on the wheel rim inside the tire, is to take up the load in the event of tire failure.
When the tire starts to rest on the safety insert, this is accompanied by a more or less pronounced deterioration in tire performance, and it is possible that this deterioration will not be noticed by the driver through the handling of the vehicle and the comfort provided by the vehicle. What is more, these inserts have a limited useful life. It is therefore essential, for his safety, that the driver should be warned as soon as a tire starts to rest on its safety insert, so that he can follow the instructions prescribed by the insert manufacturer.
A number of safety inserts that incorporate means for warning the driver that the tire is resting on the insert have already been proposed.
U.S. Pat. No. 4,262,724 in particular proposes a safety insert intended to be mounted in an assembly comprising a tire and a wheel rim and to be mounted radially externally relative to the wheel rim. This insert has a radially exterior surface which defines a radial support for the crown of the tire when the tire is deflated, and whose running radius under run-flat conditions varies between a minimum radius and a maximum radius in order to create a running vibration. More specifically, this radially exterior surface has two circumferential regions, the first having the maximum radius, the second having the minimum radius, the two regions being connected by transition zones with intermediate radii.
This patent also proposes that one or more bumps be built into the safety insert. This solution makes driving very uncomfortable especially at low speeds. All this solution does is prevent the vehicle from being instantly immobilized in the event of tire failure. By contrast, when one wishes to use the vehicle, even at a limited speed for long distances, the warning transmitted by the insert needs to be compatible with driving safely, needs not to harm the mechanical structures while at the same time being perfectly perceptible to the driver.